1. Field of the Invention
The invention generally relates to the powering of peripheral devices through a remotely terminated differential driver load supply and more specifically to powering of peripheral circuits of an HDMI transmitter from the wasted power of the HDMI transmitter driver that is terminated at the receiver.
2. Prior Art
A typical high-definition multimedia interface (HDMI) transmission system 100 is shown in FIG. 1. The HDMI system has a source side driver 110 at the transmitter, with the drivers and the peripheral circuits, and a sink side termination 120 at the receiver. The twin differential drivers NL0 and NL1 of the source transmitter 115, driving the signal lines TXN and TXP respectively, are terminated through the termination resistors R0 and R1 connected to power supply at the receiver, or sink side termination 120. The termination is, for example, to the 3.3V nominal power supply per the HDMI specification. The transmitter drivers draw current from the receiver power supply through the termination resistors that enable the signal swing as per the HDMI specification. Since the drivers are differential, they draw a constant DC current and consume power. Part of the power that is consumed is in the switching of the differential drivers and the rest is used for setting up the DC conditions of the drivers with a fixed voltage and/or current. This part of the power is typically wasted.
In the prior art, the power supply to the peripheral circuits like pre-amplifier 111, phrase-locked loop PLL 112, serializer 113, and bias circuits 114, are from the power connection to the transmitter from an external supply.
In the case of the HDMI 1.2 standard, there are four transmission channels; each channel drawing 10.0 mA nominal current from the receiver's power supply. According to the HDMI specification, the signal swing across the load termination is 0.4 to 0.6 V which leaves 2.7 V out of the typical 3.3V supply. This power is currently dissipated in setting up the DC conditions of the drivers and hence, wasted. This power is available and can be tapped to power part of the peripheral circuits in the transmitter as disclosed in this disclosure.